High temperature resins based polyesters possess desirable chemical resistance, proccessability and heat resistance. This makes them particularly well suited for demanding high performance applications.
Thermoplastic materials are known to be useful materials to produce hollow bodies, such as pipes, ducts, conduits, tubes and tubings. While hollow bodies can be manufactured by blow molding techniques, manufacturing costs and productivity can be improved by manufacturing them by melt extrusion processes. Melt extrusion processes begin by extruding a thermoplastic melt through an orifice of a die forming an extrudate capable of maintaining a desired shape. The extrudate is typically drawn into its final dimensions while maintaining the desired shape and is then quenched in air or a water bath to set the shape, thereby producing a hollow body. Hollow bodies made of thermoplastic are well known for a variety of applications, like for example in the building industry for water pipes, radiator pipes or floor-heating pipes or in automotive conduits to carry many different fluids or liquid media and are desired to display an outstanding balance of properties including thermal and mechanical resistances. All of these applications include the use of aliphatic polyamide, thermoplastic polyester elastomer, high-heat rubber composites and braided polytetrafluoroethylene (PTFE).
There is a current and general desire in the automotive field to have high temperature resistant structures since temperatures higher than 100° C., even higher than 150° C., are often reached in underhood areas of automobiles. For this reason, the use of aliphatic polyamide is limited in these high temperature applications. Whereas high-heat rubber composites and braided PTFE can be used in these higher heat environments, the structures are often complex and expensive.
Moreover, it is required that thermoplastic articles retain their structural integrity for a prolonged period in the face of the surrounding environment and deleterious conditions that are met in the automotive industry for example so that the functionality of the article is maintained until the end of its life time. However, when plastic parts are exposed to high temperatures for a prolonged period, such as in automotive under-the-hood applications or in electrical/electronics applications, the mechanical properties generally tend to decrease due to the thermo-oxidation of the polymer. This phenomenon is called heat aging. In an attempt to improve heat aging characteristics, it has been the conventional practice to add heat stabilizers and impact modifiers to thermoplastic compositions comprising polyester.
U.S. Pat. No. 3,435,093 discloses a polyethylene terephthalate (PET) composition comprising an ethylene acid copolymer, which ethylene acid copolymer may be neutralized to form the corresponding ionomer. Such a composition is said to exhibit improved elongation at room temperature. However, this polyethylene terephthalate composition does not withstand high temperatures such as those obtained under hood.
U.S. Pat. No. 7,022,768 discloses a polyester composition comprising from 60 to 99 wt-% of a thermoplastic polyester and from 1 to 40 wt-% of an impact modifier comprising a core-shell copolymer, an ethylene-unsatured epoxide copolymer, an ethylene alkyl(meth)acrylate copolymer and optionally an ionomer. Such a composition is said to exhibit shock-proof properties especially at low temperatures.
EP 0174343 discloses a polyester composition comprising from 60 to 97 wt-% of a thermoplastic polyester and from 3 to 40 wt-% of a glycidyl(meth)acrylate ethylene copolymer. Such a composition is said to exhibit high toughness especially at low temperatures.
U.S. Pat. No. 3,435,093 discloses a polyester composition comprising an ethylene acid copolymer wherein the carboxylic groups of the copolymers may be neutralized by a metal cation. Such compositions are said to exhibit improved elongation in comparison with parts made of polyester alone after a 16 hours treatment at 200° C. under nitrogen.
Unfortunately, existing technologies lead not only to a poor improvement of long-term heat aging resistance, but also the molded articles obtained thereof suffer from an unacceptable deterioration of their mechanical properties due to thermo-oxidation upon long-term high temperature exposure.
There remains a need for poly(cyclohexylene-dimethylene) terephthalate compositions that are suitable for manufacturing articles and that maintain good mechanical properties against long-term high temperature exposure.